1. Field of the Invention
The present invention relates to security paper for use as currency, negotiable instruments, documents representing monetary or property assets, passports, transcripts and any other document which because of its inherent value is subject to forgery, counterfeiting, etc., and relates to the method of manufacturing the security paper. In particular, the invention is directed to security paper having authentication indicia detectable in transmitted light but substantially imperceptible in reflected light.
2. Description of Related Art
A paper entitled "Counterfeiting Trends and Deterrent Measures" authored by the Committee on U. S. Currency, National Materials Advisory Board and published in 1987 discusses various options available to inhibit counterfeiting of currency, particularly in view of advances in high quality reprographic systems and advances in computer publishing capabilities. The paper enumerates various modifications to currency paper and to currency printing techniques which may be used to frustrate counterfeiters having access to modern high technology equipment. Among those considered most effective for currency use were various modifications of the paper substrate such as the incorporation of the security threads, water marks or other substrate modifications which would present authentication indicia in transmitted light but which would be invisible in reflected light.
While the paper mentioned above addressed currency counterfeiting, the need for security paper which would frustrate counterfeiting of other documents such as negotiable instruments, stock and bond certificates, invoices, labels, receipts, passports, property title, transcripts, licenses, lottery tickets, coupons and the like is evident. Modern computers, desktop publishing systems, optical scanners and photocopiers present forgers with a previously unavailable opportunity to reproduce illegally numerous documents having inherent value. The scope of such activities has been reported in "Desktop Forgery," Forbes, pp. 246-254 (Nov. 27, 1989), and "Forgery in the Home Office," Time, pp. 69-71 (Mar. 26, 1990). These articles indicate the urgent need for a security paper having authentication indicia which cannot be reproduced by instruments using reflected light, such as photocopiers and optical scanners.
For such security paper to effectively inhibit forgery, the authentication indicia must be substantially imperceptible not only to copying instruments using reflected light, but also to the naked eye in ambient reflected light. If authentication indicia were visible to the naked eye in reflected light, they could be placed artificially on the face of a forgery even though they were not copyable by an instrument. For authentication indicia to be effective, there must be an easy way for the authenticity of a document printed on security paper to be confirmed. This can be achieved by rendering the authentication indicia only readily visible in transmitted light.
The subject invention is directed to a security paper having authentication indicia which is not clearly visible to the eye and not reproducible by instruments using reflected light but which is detectable by being visible or optically readable in transmitted light. In a second embodiment, the authentication may be magnetically detected. The invention is also directed to the method of manufacturing the security paper which overcomes the disadvantages of the prior art processes.